Trackpad Scroll Emulator

1. What it does

Traditionally scrollbars are permanently displayed whenever an area of a webpage is scrollable. By contrast, scrollbars in OS X are hidden from sight, and revealed only when the user executes a swipe gesture with a 'magic' trackpad pointing device.

This plugin emulates OS X's UI pattern by replacing the browser's default scrollbars with a custom CSS-styled scrollbar that is only revealed when the user hovers over a scrollable element.

Modern browsers get a very accurate emulation of OS X's scrollbars, while less capable browsers miss out on a few bells and whistles such as rounded corners, opacity, and animated fades.

Options

wrapContent

By default TrackpadScrollEmulator requires minimal markup, as shown above. When initialized it will wrap the tse-contentelement in a div with the class tse-scroll-content. If you prefer to include this wrapper element directly in your markup you can switch the default behaviour off by setting the wrapContent option to false:

$('.wrapper').TrackpadScrollEmulator({ wrapContent: false });

Default value is true

autoHide

By default TrackpadScrollEmulator automatically hides the scrollbar if the user is not scrolling. You can make the scrollbar always visible by setting the autoHide option to false:

$('.wrapper').TrackpadScrollEmulator({ autoHide: false });

Default value is true

Notifying the plugin of content changes

If you later dynamically modify your content, for instance changing its height or width, or adding or removing content, you should recalculate the scrollbars like so:

$('.wrapper').TrackpadScrollEmulator('recalculate');

Destroying the plugin

To remove the plugin from your element, call its destroy method:

$('.wrapper').TrackpadScrollEmulator('destroy');

Overwriting the content dimensions

The dimensions of the tse-scrollable wrapping element determine the visible dimensions of your content. Chances are that you'll want to change the width or height of the wrapping element, which can be done using CSS or JavaScript:

.wrapper {
width: 250px; /* Example of overwiting default width */
}

The demo bundled with Trackpad Scroll Emulator demonstrates how you might dynamically alter the dimensions of tse-scrollable using JavaScript.

Non-JS fallback

Trackpad Scroll Emulator hides the browser's default scrollbars, which obviously is undesirable if the user has JavaScript disabled. To restore the browser's scrollbars you can include the following noscript element in your document's head:

4. How it works

For the most part Trackpad Scroll Emulator uses the browser's native scrolling functionality, but replaces the conventional scrollbar with a custom CSS-styled scrollbar. The plugin listens for scroll events and redraws the custom scrollbar accordingly.

Key to this technique is hiding the native browser scrollbar. In modern browsers (i.e. WebKit) this is achieved simply by giving the scrollbar a width/height of zero using the ::webkit-scrollbar and ::scrollbarpseudo selectors. In other browsers the scrollable element is made slightly wider/taller than its containing element, effectively hiding the scrollbar from view.

5. Limitations

Trackpad Scroll Emulator can currently handle vertical or horizontal scrollbars, but not both simultaneously.

6. Credits

Obviously most of the credit for this technique goes to Rdio's developers. Rdio is a Backbone application, so their solution is a combination of Backbone, Underscore, jQuery, CSS and Bujagali (their own templating system). What I have done is to recreate the same scrolling functionality using only jQuery and CSS.